The proposed studies will investigate the function of certain cell types such as mast cells and the various leukocytes in normal tissues and in diseased or experimentally modified tissues of man and laboratory animals. They will also undertake to delineate and characterize organelles within cells, to interpret the function of these structures in normal cell processes and to appraise their alteration in pathologic conditions. The contemplated investigations deal with biologic and pathologic processes in a variety of tissue sites. The objectives will be approached by employing transmission electron microscopy on ultrathin sections and surface replicas, the freeze-etch procedure, electron probe X-Ray microanalysis, scanning electron microscopy, and cytochemical procedures including particularly methods for localizing specific mucosubstances, phosphatases and ions and methods for visualizing specific antigens by immunostaining. Where methodology appears inadequate for attaining certain objectives efforts at development or modification of cytochemical techniques will be attempted. The morpho-chemical approach will be correlated with biochemical investigation of cell organelles employing cell separation and fractionation techniques and biochemical and chromatographic methods for analysis of cell proteins and mucosubstances.